Not applicable.
Not applicable.
1. Field of the Invention
The present invention relates to a device for raising and lowering items and, more particularly, to a mechanism for maintaining a parallel orientation between a base structure and a movable structure while varying the distance between the structures.
2. Background Information
This invention applies to maintaining parallelism between a base structure and a movable structure as it applies to lifting devices, lift tables, adjustable workstations, and other applications where maintaining parallelism is necessary.
Currently available lift tables are most commonly actuated by a scissor mechanism featuring arms which pivot with a mating arm in the center of their length. One end of these arms is rotatably fixed to either the top structure or the base structure of the lift, and the other end is free to move along a plane parallel to the base and the movable surface. Because of the central pivot point, large bending forces are introduced into said arms. To maintain strength and safety, these arms and structures related to them must be made of sufficient quantities of strong materials, usually steel, which results in considerable weight. These lifts suffer reduced capacity as a result of having to lift this weight in addition to the load. These lifts generally are limited in length, as the bending forces on the arms and the energy required to move the arms becomes impractically large at longer arm lengths. These lifts also are limited in terms of portability, because their mass makes them difficult to move. Also, due to this mass, these lifts need relatively larger actuation devices and more energy to operate. In some cases these devices can only operate vertically because they rely on gravity to maintain parallelism between the base and the movable structure.
Applicant has devised a mechanism for maintaining a parallel orientation between a base structure and a movable structure, while varying the distance between the structures.
The invention is a mechanism for maintaining parallel orientation between a base structure and a moveable structure. The mechanism includes a pair of opposed arm assemblies, each assembly adapted for rotatable attachment at one end to the base structure and adapted for rotatable attachment at an opposite end to the moveable structure. Each arm assembly includes at least one pair of arm members, each at least one pair of arm members pivotally mounted at one arm member end to a center shaft member, with one arm member of each at least one pair rigidly secured to a first support shaft member at an end opposite the center shaft member and another arm member of each at least one pair rigidly secured to a second support shaft member at an end opposite the center shaft member. The first support shaft member is adapted for rotatable attachment to the moveable structure, and the second support shaft member is adapted for rotatable attachment to the base structure. An actuating means for effecting movement between the center shaft members of the pair of opposed arm assemblies is present. A first mechanical timing mechanism operatively connects the first support shaft members, the first timing mechanism effecting equal and opposite rotation between the first support shaft members of the opposed arm assemblies, and a second mechanical timing mechanism operatively connects the second support shaft members, the second timing mechanism effecting equal and opposite rotation between the second support shaft members of the opposed arm assemblies. The mechanism maintains parallel orientation between the base structure and the moveable structure. In a preferred embodiment of the mechanism invention, each arm assembly includes two pairs of arm members.
In another embodiment of the invention, a lifting system for level movement is disclosed. The lifting system includes a base structure and a moveable structure, with the structures positioned in register with each other. A pair of opposed arm assemblies are positioned between the base structure and the moveable structure, with each assembly rotatably secured at one end to the base structure and rotatably secured at an opposite end to the moveable structure. Each arm assembly includes at least one pair of arm members, with each at least one pair of arm members pivotally mounted at one arm member end to a center shaft member. One arm member of each at least one pair is rigidly secured to a first support shaft member at an end opposite the center shaft member, and another arm member of each at least one pair is rigidly secured to a second support shaft member at an end opposite the center shaft member. The first support shaft member is rotatably secured to the moveable structure, and the second support shaft member is rotatably secured to the base structure. An actuating means is present for effecting movement between the center shaft members of the pair of opposed arm assemblies. A first mechanical timing mechanism operatively connects the first support shaft members, the first timing mechanism effecting equal and opposite rotation between the first support shaft members of the opposed arm assemblies, and a second mechanical timing mechanism operatively connects the second support shaft members, the second timing mechanism effecting equal and opposite rotation between the second support shaft members of the opposed arm assemblies, thereby providing parallel movement between the base structure and the moveable structure. In a preferred embodiment of the lifting system invention, each arm assembly includes two pairs of arm members.